Coated cutting tool

ABSTRACT

An object of the invention is to provide a coated cutting tool whose tool life can be extended by having excellent wear resistance and fracture resistance. The coated cutting tool includes: a substrate; and a coating layer formed on a surface of the substrate, in which the coating layer includes a lower layer, an intermediate layer, and an upper layer in this order from a substrate side to a surface side of the coating layer, the lower layer includes one or more Ti compound layers formed of a specific Ti compound, the intermediate layer contains TiCNO, TiCO, or TiAlCNO, the upper layer contains α-type Al2O3, an average thickness of the lower layer is 2.0 μm or more and 8.0 μm or less, an average thickness of the intermediate layer is 0.5 μm or more and 2.0 μm or less and is 10% or more and 20% or less of an average thickness of the entire coating layer, an average thickness of the upper layer is 0.8 μm or more and 6.0 μm or less, and in the intermediate layer, a ratio of a length of CSL grain boundaries and a ratio of a length of Σ3 grain boundaries are in specific ranges.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2020-117692 on (Jul. 8, 2020), the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a coated cutting tool.

Description of Related Art

In the related art, it is well known that a coated cutting tool, inwhich a coating layer is vapor-deposited on a surface of a substratemade of cemented carbide by a chemical vapor deposition method and has atotal thickness of 3 μm to 20 μm, is used for cutting steel, cast iron,and the like. As the above-described coating layer, there has beenknown, for example, a coating layer formed of one type of single layeror two or more types of multiple layers selected from the groupconsisting of carbides, nitrides, carbonitrides, oxycarbides, andoxycarbonitrides of Ti, and aluminum oxides.

Further, it is known that in order to improve adhesion between a Ticarbonitride layer and an aluminum oxide layer formed by the chemicalvapor deposition method, a (Ti, Al) (C, N, O) layer, a Tioxycarbonitride layer, and the like are formed.

For example, WO 2017/090765 (PTL 1) describes a cutting tool including asubstrate and a coating layer located on a surface of the substrate. Thecoating layer includes a lower layer containing titanium nitride, anupper layer containing aluminum oxide, having an α-type crystalstructure, which is located above the lower layer, and an intermediatelayer located between the lower layer and the upper layer. Theintermediate layer includes a first layer containingTiC_(x1)N_(y1)O_(z1) (0≤x1<1, 0≤y1<1, 0<z1<1, x1+y1+z1=1) and adjacentto the lower layer, a second layer containing TiC_(x2)N_(y2)O_(z2)(0≤x2<1, 0≤y2<1, 0<z2<1, x2+y2+z2=1) and adjacent to the upper layer,and a third layer located between the first layer and the second layerand containing TiC_(x3)N_(y3)O_(z3) (0≤x3<1, 0≤y3<1, 0≤z3<1,x3+y3+z3=1), and z1>z3 and z2>z3.

For example, JP-T-2014-526391 (PTL 2) describes a cutting tool insertincluding a substrate formed of a superhard material such as cementedcarbide, cermet, ceramics, steel, or cubic boron nitride (CBN) and acoating having a total thickness of 5 μm to 40 μm. The coating includesone or more heat-resistant layers in which at least one layer is anα-Al₂O₃ layer having a thickness of 1 μm to 20 μm. Here, a length ofΣ3-type crystal grain boundaries in the at least one α-Al₂O₃ layer ismore than 80% of a total length of Σ3, Σ7, Σ11, Σ17, Σ19, Σ21, Σ23, andΣ29-type crystal grain boundaries (=Σ3-29-type crystal grainboundaries), and the crystal grain boundary character distribution ismeasured by EBSD.

In cutting processing in recent years, high speed, high feed, and deepcutting have become more remarkable, and it is required to improve wearresistance and fracture resistance of tools as compared with the toolsin the related art. In particular, in high speed, high feed, and deepcutting for stainless steel, cutting processing in which a load acts ona coated cutting tool is increasing. In such harsh cutting conditions,since adhesion between an aluminum oxide layer and a Ti compound layeras a lower layer in a coating layer is insufficient for the tool in therelated art, a fracture occurs due to the peeling of the aluminum oxidelayer. There is a problem that the tool life cannot be extended becauseof the above reason. Further, since stainless steel undergoes processinghardening and becomes harder, it is difficult to extend the tool lifedue to insufficient wear resistance even if the adhesion is improved.

On the other hand, it is known that a TiCNO layer in PTL 1 is formed inorder to improve the adhesion between the aluminum oxide layer and theTi compound layer as the lower layer, but in stainless steel processingwhere processing hardening occurs, the adhesion is insufficient andthere is room for improvement. Further, PTL 2 examines the length of theΣ3-type crystal grain boundaries, but does not consider crystal grainboundaries in a bond layer between a TiCN layer and the α-Al₂O₃ layer.Therefore, in stainless steel processing where processing hardeningoccurs, the adhesion and the wear resistance are insufficient and thereis room for improvement.

SUMMARY

The invention has been made in view of the above circumstances, and anobject of the invention is to provide a coated cutting tool whose toollife can be extended by having excellent wear resistance and fractureresistance.

After conducting research on extending the tool life of a coated cuttingtool from the above viewpoint, the inventor has found that adhesion isfurther improved by setting a ratio of a length of CSL grain boundariesand a ratio of a length of Σ3 grain boundaries in an intermediate layerbetween a lower layer containing a Ti compound layer and an upper layercontaining α-type Al₂O₃ to a specific range, and thereby, damage to theupper layer containing α-type Al₂O₃ is prevented and an effect of theupper layer containing α-type Al₂O₃ lasts longer than that in therelated art, so it is possible to improve wear resistance, and as aresult, the tool life of the coated cutting tool can be extended. Thus,the invention has been completed.

That is, the gist of the invention is as follows.

[1]

A coated cutting tool including:

a substrate; and

a coating layer formed on a surface of the substrate, in which

the coating layer includes a lower layer, an intermediate layer, and anupper layer in this order from a substrate side to a surface side of thecoating layer,

the lower layer includes one or more Ti compound layers formed of a Ticompound containing Ti and at least one element selected from the groupconsisting of C, N, and B,

the intermediate layer contains TiCNO, TiCO, or TiAlCNO,

the upper layer contains α-type Al₂O₃,

an average thickness of the lower layer is 2.0 μm or more and 8.0 μm orless,

an average thickness of the intermediate layer is 0.5 μm or more and 2.0μm or less and is 10% or more and 20% or less of an average thickness ofthe entire coating layer,

an average thickness of the upper layer is 0.8 μm or more and 6.0 μm orless, and

in the intermediate layer, a ratio of a length of CSL grain boundariesto a total length 100% of a total grain boundary is 20% or more and 60%or less, and a ratio of a length of Σ3 grain boundaries to a totallength 100% of the CSL grain boundaries is 50% or more and 90% or less.

[2]

The coated cutting tool according to [1], in which

the ratio of the length of the Σ3 grain boundaries to the total length100% of the CSL grain boundaries is 60% or more and 90% or less.

[3]

The coated cutting tool according to [1] or [2], in which

the coating layer includes an outer layer on the upper layer and on aside opposite to the substrate side,

the outer layer includes a Ti compound layer formed of a Ti compoundcontaining Ti and at least one element selected from the groupconsisting of C, N, and B, and

an average thickness of the outer layer is 0.2 μm or more and 4.0 μm orless.

[4]

The coated cutting tool according to any one of [1] to [3], in which

the average thickness of the entire coating layer is 5.0 μm or more and20.0 μm or less.

[5]

The coated cutting tool according to any one of [1] to [4], in which

the Ti compound layer included in the lower layer is at least oneselected from the group consisting of a TiN layer formed of TiN, a TiClayer formed of TiC, a TiCN layer formed of TiCN, and a TiB₂ layerformed of TiB₂.

[6]

The coated cutting tool according to any one of [1] to [5], in which

the substrate is any one of cemented carbide, cermet, ceramics, or acubic boron nitride sintered body.

Advantageous Effects of the Invention

According to the invention, it is possible to provide a coated cuttingtool whose tool life can be extended by having excellent wear resistanceand fracture resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a schematic view showing an example of a coated cuttingtool according to the invention.

DETAILED DESCRIPTION

Hereinafter, an embodiment for implementing the invention (hereinafter,simply referred to as “the present embodiment”) will be described indetail with reference to the drawings as necessary, but the invention isnot limited to the following embodiment. The invention can be modifiedin various ways without departing from the gist thereof. Unlessotherwise specified, a positional relationship such as up, down, left,and right in the drawing is based on a positional relationship shown inthe drawing. Furthermore, a dimensional ratio in the drawing is notlimited to a ratio shown.

A coated cutting tool of the present embodiment includes: a substrate;and a coating layer formed on a surface of the substrate. The coatinglayer includes a lower layer, an intermediate layer, and an upper layerin this order from a substrate side to a surface side of the coatinglayer, the lower layer includes one or more Ti compound layers formed ofa Ti compound containing Ti and at least one element selected from thegroup consisting of C, N, and B, the intermediate layer contains TiCNO(Ti carbonitride), TiCO (Ti carbide), or TiAlCNO (Ti and Aloxycarbonitride), the upper layer contains α-type Al₂O₃, an averagethickness of the lower layer is 2.0 μm or more and 8.0 μm or less, anaverage thickness of the intermediate layer is 0.5 μm or more and 2.0 μmor less and is 10% or more and 20% or less of an average thickness ofthe entire coating layer, an average thickness of the upper layer is 0.8μm or more and 6.0 μm or less, and in the intermediate layer, a ratio ofa length of CSL grain boundaries to a total length 100% of a total grainboundary is 20% or more and 60% or less, and a ratio of a length of Σ3grain boundaries to a total length 100% of the CSL grain boundaries is50% or more and 90% or less.

With the above configuration, wear resistance and fracture resistance ofthe coated cutting tool of the present embodiment can be improved, andas a result, the tool life can be extended. Factors for improving thewear resistance and the fracture resistance of the coated cutting toolof the present embodiment are considered as follows. However, theinvention is not limited to the following factors. That is, first, inthe coated cutting tool of the present embodiment, the lower layer ofthe coating layer includes one or more Ti compound layers formed of a Ticompound containing Ti and at least one element selected from the groupconsisting of C, N, and B. When the coated cutting tool of the presentembodiment includes such a lower layer between the substrate and theintermediate layer, the wear resistance and the adhesion are improved.Further, in the coated cutting tool of the present embodiment, when theaverage thickness of the lower layer is 2.0 μm or more, the wearresistance is improved, and on the other hand, when the averagethickness of the lower layer is 8.0 μm or less, the fracture resistanceis improved mainly due to the prevention of peeling of the coatinglayer.

Further, in the coated cutting tool of the present embodiment, thecoating layer includes the intermediate layer containing TiCNO, TiCO, orTiAlCNO. When such an intermediate layer is formed under the upper layercontaining α-type Al₂O₃, the adhesion is improved. Further, when theaverage thickness of the intermediate layer is 0.5 μm or more, a surfaceof the lower layer can be uniformly covered, and therefore, the adhesionis improved and a fracture caused by peeling can be prevented. On theother hand, when the average thickness of the intermediate layer is 2.0μm or less, the occurrence of the fracture can be prevented and thefracture resistance is improved. Further, in the coated cutting tool ofthe present embodiment, the average thickness of the intermediate layeris 10% or more and 20% or less of the average thickness of the entirecoating layer. When the average thickness of the intermediate layer is10% or more of the average thickness of the entire coating layer, theratio of the length of the CSL grain boundaries is increased, andtherefore, the adhesion is further improved and the fracture resistanceis excellent. Further, when the average thickness of the intermediatelayer is 10% or more of the average thickness of the entire coatinglayer, the fracture resistance is improved by reducing a ratio of alayer such as the lower layer or the upper layer having hardness higherthan that of the intermediate layer. On the other hand, when the averagethickness of the intermediate layer is 20% or less of the averagethickness of the entire coating layer, the occurrence of the fracturecan be prevented by preventing a decrease in strength of the coatinglayer. Further, in the coated cutting tool of the present embodiment, inthe intermediate layer, the ratio of the length of the CSL grainboundaries to the total length 100% of the total grain boundary is 20%or more and 60% or less. In the intermediate layer, when the ratio ofthe length of the CSL grain boundaries to the total length 100% of thetotal grain boundary is 20% or more, a ratio of grain boundaries havingrelatively low grain boundary energy increases, and therefore,mechanical properties of the intermediate layer are improved. On theother hand, in the intermediate layer, when the ratio of the length ofthe CSL grain boundaries to the total length 100% of the total grainboundary is 60% or less, coarse graining of crystal grains can beprevented, and therefore, chipping resistance is excellent. In thepresent embodiment, the total length of the total grain boundary is asum of the length of the CSL grain boundaries and a length of othergeneral crystal grain boundaries. Further, in the coated cutting tool ofthe present embodiment, in the intermediate layer, the ratio of thelength of the Σ3 grain boundaries to the total length 100% of the CSLgrain boundaries is 50% or more and 90% or less. In the intermediatelayer, when the ratio of the length of the Σ3 grain boundaries to thetotal length 100% of the CSL grain boundaries is 50% or more, itindicates that a ratio of crystal grain boundaries having relatively lowgrain boundary energy is large. In the coated cutting tool of thepresent embodiment, when the grain boundary energy is low, themechanical properties are improved, and therefore crater wear resistanceis improved. On the other hand, when the ratio of the length of the Σ3grain boundaries to the total length 100% of the CSL grain boundaries is90% or less, production is easy.

Further, in the coated cutting tool of the present embodiment, theaverage thickness of the upper layer containing α-type Al₂O₃ is 0.8 μmor more and 6.0 μm or less. When the average thickness of the upperlayer containing α-type Al₂O₃ is 0.8 μm or more, crater wear resistanceon a rake face of the coated cutting tool is further improved. When theaverage thickness of the upper layer containing α-type Al₂O₃ is 6.0 μmor less, the peeling of the coating layer is further prevented, and thefracture resistance of the coated cutting tool tends to be furtherimproved.

Then, by combining these configurations, it is considered that the wearresistance and the fracture resistance of the coated cutting tool of thepresent embodiment are improved, and as a result, the tool life can beextended.

The FIGURE is a schematic cross-sectional view showing an example of thecoated cutting tool according to the present embodiment. A coatedcutting tool 7 includes a substrate 1 and a coating layer 6 formed on asurface of the substrate 1, and in the coating layer 6, a lower layer 2,an intermediate layer 3, an upper layer 4, and an outer layer 5 arelaminated in this order in an upward direction (from the substrate sideto the surface side of the coating layer).

The coated cutting tool of the present embodiment includes the substrateand the coating layer formed on the surface of the substrate. Specificexamples of types of the coated cutting tool include an indexablecutting insert for milling or turning, a drill, and an end mill.

The substrate used in the present embodiment is not particularly limitedas long as the substrate can be used as a substrate for a coated cuttingtool. Examples of such a substrate include cemented carbide, cermet,ceramics, a cubic boron nitride sintered body, a diamond sintered body,and high speed steel. Among the above, it is preferable the substrate isany one of cemented carbide, cermet, ceramics, and a cubic boron nitridesintered body because the coated cutting tool is more excellent in thewear resistance and the fracture resistance, and from the sameviewpoint, it is more preferable that the substrate is cemented carbide.

The surface of the substrate may be modified. For example, when thesubstrate is made of cemented carbide, a β-free layer may be formed onthe surface thereof. Further, when the substrate is made of cermet, acured layer may be formed on the surface thereof. Even if the surface ofthe substrate is modified as described above, the effects of theinvention can be achieved.

The coating layer used in the present embodiment preferably has theaverage thickness of 5.0 μm or more and 20.0 μm or less, and therefore,the wear resistance is improved. In the coated cutting tool of thepresent embodiment, when the average thickness of the entire coatinglayer is 5.0 μm or more, the wear resistance is improved, and when theaverage thickness of the entire coating layer is 20.0 μm or less, thefracture resistance is improved mainly due to the prevention of peelingof the coating layer. In particular, in stainless steel processing, thecoating layer is likely to be peeled off due to a work material beingwelded to the coated cutting tool and then separated (peeled). In orderto prevent the peeling, it is more preferable that the average thicknessof the entire coating layer is 19.0 μm or less. The average thickness ofeach layer or the entire coating layer in the coated cutting tool of thepresent embodiment is obtained by measuring the thickness of each layeror the thickness of the entire coating layer from three or more crosssections in each layer or the entire coating layer, and calculating anarithmetic mean value.

[Lower Layer]

The lower layer used in the present embodiment includes one or more Ticompound layers formed of a Ti compound containing Ti and at least oneelement selected from the group consisting of C, N, and B. When thecoated cutting tool of the present embodiment includes such a lowerlayer between the substrate and the intermediate layer, the wearresistance and the adhesion are improved.

Examples of the Ti compound layer include a TiC layer formed of TiC, aTiN layer formed of TiN, a TiCN layer formed of TiCN, and a TiB₂ layerformed of TiB₂.

The lower layer may include one layer or multiple layers (for example,two or three layers), and preferably includes multiple layers, morepreferably includes two or three layers, and still more preferablyincludes two layers. The lower layer preferably includes at least onelayer selected from the group consisting of a TiN layer, a TiC layer, aTiCN layer, and a TiB₂ layer from the viewpoint of further improving thewear resistance and the adhesion. Further, in the coated cutting tool ofthe present embodiment, when at least one layer of the lower layer is aTiCN layer, the wear resistance tends to be further improved.

Further, in the coated cutting tool of the present embodiment, when atleast one layer of the lower layer is a TiN layer, and the TiN layer isformed on the surface of the substrate, the adhesion tends to be furtherimproved. When the lower layer includes two layers, a TiC layer or a TiNlayer may be formed as a first layer on the surface of the substrate,and a TiCN layer may be formed as a second layer on the surface of thefirst layer. Among the above, the lower layer may be formed with a TiNlayer as the first layer on the surface of the substrate and formed witha TiCN layer as the second layer on the surface of the first layer.

The average thickness of the lower layer used in the present embodimentis 2.0 μm or more and 8.0 μm or less. In the coated cutting tool of thepresent embodiment, when the average thickness of the lower layer is 2.0μm or more, the wear resistance is improved. On the other hand, in thecoated cutting tool of the present embodiment, when the averagethickness of the lower layer is 8.0 μm or less, the fracture resistanceis improved mainly due to the prevention of the peeling of the coatinglayer. From the same viewpoint, the average thickness of the lower layeris preferably 2.1 μm or more and 7.9 μm or less, and more preferably 2.2μm or more and 6.0 μm or less.

The average thickness of the TiC layer or the TiN layer is preferably0.05 μm or more and 1.0 μm or less from the viewpoint of furtherimproving the wear resistance and the fracture resistance. From the sameviewpoint, the average thickness of the TiC layer or the TiN layer ismore preferably 0.1 μm or more and 0.5 μm or less, and still morepreferably 0.1 μm or more and 0.2 μm or less.

The average thickness of the TiCN layer is preferably 2.0 μm or more and10.0 μm or less from the viewpoint of further improving the wearresistance and the fracture resistance. From the same viewpoint, theaverage thickness of the TiCN layer is more preferably 3.0 μm or moreand 9.0 μm or less, and still more preferably 3.2 μm or more and 7.8 μmor less.

The Ti compound layer is a layer formed of a Ti compound containing Tiand at least one element selected from the group consisting of C, N, andB, and may contain a small amount of components other than the aboveelements as long as the Ti compound layer achieves the effects of thelower layer.

[Intermediate Layer]

The intermediate layer used in the present embodiment contains TiCNO,TiCO, or TiAlCNO. The intermediate layer is preferably a TiCNO layerformed of TiCNO, a TiCO layer formed of TiCO, or a TiAlCNO layer formedof TiAlCNO, and is preferably a TiCNO layer or a TiCO layer. When suchan intermediate layer is formed so as to be in contact with the upperlayer containing α-type Al₂O₃, the adhesion is further improved.

The average thickness of the intermediate layer used in the presentembodiment is 0.5 μm or more and 2.0 μm or less. When the averagethickness of the intermediate layer is 0.5 μm or more, the surface ofthe lower layer can be uniformly covered, and therefore, the adhesion isimproved and the fracture caused by peeling can be prevented. On theother hand, when the average thickness of the intermediate layer is 2.0μm or less, the occurrence of the fracture can be prevented and thefracture resistance is improved. From the same viewpoint, the averagethickness of the intermediate layer is preferably 0.8 μm or more and 1.8μm or less.

Further, in the coated cutting tool of the present embodiment, theaverage thickness of the intermediate layer is 10% or more and 20% orless of the average thickness of the entire coating layer. When theaverage thickness of the intermediate layer is 10% or more of theaverage thickness of the entire coating layer, the ratio of the lengthof the CSL grain boundaries is increased, and therefore, the adhesion isfurther improved and the fracture resistance is excellent. Further, whenthe average thickness of the intermediate layer is 10% or more of theaverage thickness of the entire coating layer, the fracture resistanceis improved by reducing a ratio of a layer such as the lower layer orthe upper layer that tends to have hardness higher than that of theintermediate layer. On the other hand, when the average thickness of theintermediate layer is 20% or less of the average thickness of the entirecoating layer, the occurrence of the fracture can be prevented bypreventing a decrease in strength of the coating layer. From the sameviewpoint, the average thickness of the intermediate layer is preferably18.8% or less of the average thickness of the entire coating layer.

Further, in the coated cutting tool of the present embodiment, in theintermediate layer, the ratio of the length of the CSL grain boundariesto the total length 100% of the total grain boundary is 20% or more and60% or less. In the intermediate layer, when the ratio of the length ofthe CSL grain boundaries to the total length 100% of the total grainboundary is 20% or more, a ratio of grain boundaries having relativelylow grain boundary energy increases, and therefore, the mechanicalproperties of the intermediate layer are improved. On the other hand, inthe intermediate layer, when the ratio of the length of the CSL grainboundaries to the total length 100% of the total grain boundary is 60%or less, coarse graining of crystal grains can be prevented, andtherefore, the chipping resistance is excellent. In the presentembodiment, the total length of the total grain boundary is a totallength of the length of the CSL grain boundaries and the length of theother general crystal grain boundaries. From the same viewpoint, in theintermediate layer, the ratio of the length of the CSL grain boundariesto the total length 100% of the total grain boundary is preferably 21%or more and 58% or less, and more preferably 22% or more and 56% orless.

Further, in the coated cutting tool of the present embodiment, in theintermediate layer, the ratio of the length of the Σ3 grain boundariesto the total length 100% of the CSL grain boundaries is 50% or more and90% or less. In the intermediate layer, when the ratio of the length ofthe Σ3 grain boundaries to the total length 100% of the CSL grainboundaries is 50% or more, it indicates that the ratio of the crystalgrain boundaries having relatively low grain boundary energy is large.In the coated cutting tool of the present embodiment, when the grainboundary energy is low, the mechanical properties are improved, andtherefore, the crater wear resistance is improved. On the other hand,when the ratio of the length of the Σ3 grain boundaries to the totallength 100% of the CSL grain boundaries is 90% or less, production iseasy. From the same viewpoint, in the intermediate layer, the ratio ofthe length of the Σ3 grain boundaries to the total length 100% of theCSL grain boundaries is preferably 54% or more and 90% or less, morepreferably 60% or more and 90% or less, and still more preferably 60% ormore and 86% or less.

The intermediate layer used in the present embodiment has crystal grainboundaries having relatively high grain boundary energy and crystalgrain boundaries having relatively low grain boundary energy. Normally,since the arrangement of atoms is irregularly disordered and randomlyarranged, the crystal grain boundaries have relatively high grainboundary energy with many gaps. On the other hand, some crystal grainboundaries have regular arrangement of atoms and few gaps, and suchcrystal grain boundaries have relatively low grain boundary energy. Atypical example of a crystal grain boundary having such relatively lowgrain boundary energy is a coincidence site lattice crystal grainboundary (hereinafter, referred to as a “CSL crystal grain boundary” andalso referred to as a “CSL grain boundary”). Crystal grain boundarieshave a significant effect on important sintering processes such asdensification, creep, and diffusion, as well as on electrical, optical,and mechanical properties. The importance of crystal grain boundariesdepends on several factors, such as a crystal grain boundary density ina material, a chemical composition at an interface, and acrystallographic texture, that is, a crystal grain boundary planeorientation and a crystal grain misorientation. The CSL crystal grainboundaries play a special role. An Σ value is known as an index showinga degree of distribution of the CSL crystal grain boundaries, and isdefined as a ratio of a crystal lattice point density of two crystalgrains that are in contact with each other at a crystal grain boundaryto a density of matching lattice points when both crystal lattices areoverlapped. For simple structures, it is generally accepted that grainboundaries having a low Σ value tend to have low interfacial energy andspecial properties. Therefore, controlling of a ratio of the CSL crystalgrain boundaries and distribution of crystal grain misorientations isconsidered to be important for the properties of the intermediate layerand improvement thereof.

In recent years, SEM-based technology known as EBSD has been used tostudy crystal grain boundaries in a material. EBSD is based on automaticanalysis of Kikuchi diffraction patterns generated by backscatteredelectrons.

For each crystal grain of a target material, a crystallographicorientation is determined after indexing the corresponding diffractionpattern. By using EBSD together with commercially available software,tissue analysis and determination of grain boundary characterdistribution (GBCD) can be performed relatively easily. By measuring andanalyzing the interface using EBSD, it is possible to clarify themisorientations of the crystal grain boundaries in a sample populationhaving a large interface. Usually, the distribution of themisorientations is related to the treatment and/or physical propertiesof the material. The misorientations of the crystal grain boundaries areobtained from normal orientation parameters such as an Euler angle, anangle/axis pair, or a Rodriguez vector.

The CSL crystal grain boundaries of the intermediate layer usuallyinclude grain boundaries such as Σ5 grain boundaries, Σ7 grainboundaries, Σ9 grain boundaries, Σ11 grain boundaries, Σ13 grainboundaries, Σ15 grain boundaries, Σ17 grain boundaries, Σ19 grainboundaries, Σ21 grain boundaries, Σ23 grain boundaries, Σ25 grainboundaries, Σ27 grain boundaries, and Σ29 grain boundaries in additionto the Σ3 grain boundaries. The Σ3 grain boundaries are considered tohave the lowest grain boundary energy among the CSL crystal grainboundaries of the intermediate layer. Here, the length of the Σ3 grainboundaries indicates the total length of the Σ3 grain boundaries in afield of view (specific region) observed by an SEM equipped with EBSD.The Σ3 grain boundaries have a higher coincidence site lattice pointdensity and lower grain boundary energy than those of other CSL crystalgrain boundaries. In other words, the Σ3 grain boundaries are CSLcrystal grain boundaries having many matching lattice points, and twocrystal grains having the Σ3 grain boundaries as the grain boundariesbehave like single crystals or twin crystals, and the crystal grainstend to be large. Then, as the crystal grains are larger, coatingproperties such as chipping resistance tend to deteriorate.

Here, the total grain boundary is a sum of the CSL crystal grainboundaries and the crystal grain boundaries other than the CSL crystalgrain boundaries. Hereinafter, the grain boundaries other than the CSLcrystal grain boundaries are referred to as “general crystal grainboundaries”. The general crystal grain boundaries are remaining grainboundaries excluding the CSL crystal grain boundaries from the totalgrain boundary of the crystal grains in the intermediate layer whenobserved with an SEM equipped with EBSD. Therefore, the “total length ofthe total grain boundary” can be expressed as the “sum of the length ofthe CSL crystal grain boundaries and the length of the general crystalgrain boundaries”.

In the present embodiment, the ratio of the length of the CSL grainboundaries to the total length 100% of the total grain boundary in theintermediate layer and the ratio of the length of the Σ3 grainboundaries to the total length 100% of the CSL grain boundaries can becalculated as follows.

In the coated cutting tool, a cross section of the intermediate layer isexposed in a direction perpendicular to the surface of the substrate toobtain an observation surface. Examples of a method for exposing thecross section of the intermediate layer include cutting and polishing.Of these, polishing is preferred from the viewpoint of making theobservation surface of the intermediate layer smoother. In particular,the observation surface is preferably a mirror surface from theviewpoint of being smoother. A method for obtaining a mirror observationsurface of the intermediate layer is not particularly limited, andexamples thereof include a method of polishing using diamond paste orcolloidal silica, ion milling, and the like.

Then, the above observation surface is observed by an SEM equipped withEBSD. As the observation region, it is preferable to observe a flatsurface (a flank and the like).

As the SEM, SU6600 (manufactured by Hitachi High-Tech Corporation)equipped with EBSD (manufactured by TexSEM Laboratories Inc.) is used.

The normal of the observation surface is tilted 70° with respect to anincident beam, and the analysis is performed by emitting an electronbeam with an acceleration voltage of 15 kV and an irradiation current of1.0 nA. Data collection is performed in steps of 0.1 μm/step for a pointcorresponding to a surface region having a length of 80% of thethickness of the intermediate layer×10 μm ((a length of 80% of thethickness of the intermediate layer (μm)×10)×100) on the observationsurface. The data collection is performed for the surface region at 5fields of view (a length of 80% of the thickness of the intermediatelayer×10 μm), and an average value is calculated.

Data processing is performed using commercially available software. TheCSL crystal grain boundaries corresponding to any Σ value are counted,and can be confirmed by expressing a ratio of each type of grainboundary as the ratio to the total grain boundary. From the above, thelength of the Σ3 grain boundaries, the length of the CSL grainboundaries, and the total length of the total grain boundary areobtained, and the ratio of the length of the CSL grain boundaries to thetotal length 100% of the total grain boundary and the ratio of thelength of the Σ3 grain boundaries to the total length 100% of the CSLgrain boundaries can be calculated.

In the present embodiment, the intermediate layer may contain TiCNO,TiCO, or TiAlCNO, and may or may not contain components other thanTiCNO, TiCO, or TiAlCNO as long as the effects of the invention areachieved.

[Upper Layer]

The upper layer used in the present embodiment contains α-type Al₂O₃. Inthe coated cutting tool of the present embodiment, since the upper layercontains α-type Al₂O₃, the coated cutting tool becomes hard, andtherefore, the wear resistance is improved. Further, in the coatedcutting tool of the present embodiment, the upper layer containingα-type Al₂O₃ is provided on the intermediate layer and on the sideopposite to the substrate side. In the coated cutting tool of thepresent embodiment, since the upper layer containing α-type Al₂O₃ isprovided on the intermediate layer containing TiCNO, TiCO or TiAlCNO andon the side opposite to the substrate side, the adhesion of the entirecoating layer is improved. Accordingly, in the coated cutting tool ofthe present embodiment, the fracture caused by peeling can be preventedin particular.

Further, in the coated cutting tool of the present embodiment, theaverage thickness of the upper layer containing α-type Al₂O₃ is 0.8 μmor more and 6.0 μm or less. When the average thickness of the upperlayer containing α-type Al₂O₃ is 0.8 μm or more, the crater wearresistance on the rake face of the coated cutting tool is furtherimproved. When the average thickness of the upper layer containingα-type Al₂O₃ is 6.0 μm or less, the peeling of the coating layer isfurther prevented, and the fracture resistance of the coated cuttingtool tends to be further improved. From the same viewpoint, the averagethickness of the upper layer is preferably 1.0 μm or more and 6.0 μm orless, and more preferably 2.0 μm or more and 4.0 μm or less.

In the present embodiment, the intermediate layer may contain α-typealuminum oxide (α-type Al₂O₃), and may or may not contain componentsother than α-type aluminum oxide (α-type Al₂O₃) as long as the effectsof the invention are achieved.

[Outer Layer]

In the coated cutting tool of the present embodiment, it is preferablethat the coating layer includes an outer layer provided on the upperlayer and on the side opposite to the substrate side.

The outer layer used in the present embodiment preferably includes a Ticompound layer formed of a Ti compound containing Ti and at least oneelement selected from the group consisting of C, N, and B. Examples ofthe Ti compound layer include a TiC layer formed of TiC, a TiN layerformed of TiN, a TiCN layer formed of TiCN, and a TiB₂ layer formed ofTiB₂.

Of these, the outer layer used in the present embodiment preferablyincludes a Ti compound layer such as a TiN layer or a TiCN layer. In thecoated cutting tool of the present embodiment, since the outer layerincludes a Ti compound layer such as a TiN layer or a TiCN layer, a usedcorner tends to be easily identified.

The average thickness of the outer layer used in the present embodimentis preferably 0.2 μm or more and 4.0 μm or less, and more preferably 0.3μm or more and 3.0 μm or less. When the average thickness of the outerlayer is equal to or more than the lower limit value, the effect ofhaving the outer layer can be more effectively and surely obtained, andwhen the average thickness of the outer layer is equal to or less thanthe upper limit value, the fracture resistance of the coated cuttingtool tends to be further improved mainly due to the fact that thepeeling of the coating layer is further prevented.

In the present embodiment, the outer layer may or may not containcomponents other than the Ti compound such as TiN and TiCN as long asthe effects of the invention are achieved.

In the coated cutting tool of the present embodiment, each layer formingthe coating layer may be formed by a chemical vapor deposition method ora physical vapor deposition method. Specific examples of a method forforming each layer include the following methods. However, the method offorming each layer is not limited thereto.

(Chemical Vapor Deposition Method)

(Lower Layer Forming Step)

As the lower layer, for example, a Ti compound layer formed of a Ticompound containing Ti and at least one element selected from the groupconsisting of C, N, and B can be formed as follows.

For example, when the Ti compound layer is a Ti nitride layer(hereinafter, also referred to as a “TiN layer”), the Ti compound layercan be formed by a chemical vapor deposition method in which a rawmaterial composition is set to TiCl₄: 5.0 mol % to 10.0 mol %, N₂: 20mol % to 60 mol %, and H₂: balance, the temperature is set to 850° C. to950° C., and the pressure is set to 300 hPa to 400 hPa.

When the Ti compound layer is a Ti carbide layer (hereinafter, alsoreferred to as a “TiC layer”), the Ti compound layer can be formed by achemical vapor deposition method in which a raw material composition isset to TiCl₄: 1.5 mol % to 3.5 mol %, CH₄: 3.5 mol % to 5.5 mol %, H₂:balance, the temperature is set to 950° C. to 1050° C., and the pressureis set to 70 hPa to 80 hPa.

When the Ti compound layer is a Ti carbonitride layer (hereinafter, alsoreferred to as a “TiCN layer”), the Ti compound layer can be formed by achemical vapor deposition method in which a raw material composition isset to TiCl₄: 5.0 mol % to 7.0 mol %, CH₃CN: 0.5 mol % to 1.5 mol %, H₂:balance, the temperature is set to 800° C. to 900° C., and the pressureis set to 60 hPa to 80 hPa.

(Intermediate Layer Forming Step)

As the intermediate layer, for example, a compound layer formed ofTiCNO, TiCO, or TiAlCNO can be formed as follows.

When the compound layer is a Ti oxycarbonitride layer (hereinafter, alsoreferred to as a “TiCNO layer”), the compound layer can be formed by achemical vapor deposition method in which a raw material composition isset to TiCl₄: 3.5 mol % to 5.5 mol %, CO: 0.5 mol % to 1.5 mol %, N₂: 20mol % to 60 mol %, HCl: 2.0 mol % to 5.0 mol %, H₂: balance, thetemperature is set to 950° C. to 1050° C., and the pressure is set to 50hPa to 150 hPa.

When the compound layer is a Ti oxycarbide layer (hereinafter, alsoreferred to as a “TiCO layer”), the compound layer can be formed by achemical vapor deposition method in which a raw material composition isset to TiCl₄: 4.0 mol % to 6.0 mol %, CO: 0.5 mol % to 1.5 mol %, HCl:2.0 mol % to 4.0 mol %, H₂: balance, the temperature is set to 950° C.to 1050° C., and the pressure is set to 50 hPa to 150 hPa.

When the compound layer is a Ti and Al oxycarbonitride layer(hereinafter, also referred to as a “TiAlCNO layer”), the compound layercan be formed by a chemical vapor deposition method in which a rawmaterial composition is set to TiCl₄: 4.0 mol % to 6.0 mol %, CO: 0.3mol % to 1.3 mol %, AlCl₃: 1.5 mol % to 3.5 mol %, N₂: 20 mol % to 60mol %, HCl: 4.0 mol % to 6.0 mol %, H₂: balance, the temperature is setto 950° C. to 1050° C., and the pressure is set to 50 hPa to 150 hPa.

In the intermediate layer, in order to set the ratio of the length ofthe CSL grain boundaries to the total length 100% of the total grainboundary within the above-described specific range, in an intermediatelayer forming step, the pressure may be controlled, the averagethickness of the intermediate layer may be controlled, a ratio of H₂ inthe raw material composition may be controlled, or HCl may beintroduced. More specifically, the ratio of the length of the CSL grainboundaries in the intermediate layer can be increased by lowering thepressure or increasing the ratio of H₂ in the raw material compositionin the intermediate layer forming step. Further, by increasing theaverage thickness of the intermediate layer, the ratio of the length ofthe CSL grain boundaries in the intermediate layer can be increased.Further, by introducing HCl in the intermediate layer forming step, theratio of the length of the CSL grain boundaries in the intermediatelayer can be set to be equal to or less than the upper limit value ofthe above-described specific range.

Further, in the intermediate layer, in order to set the ratio of thelength of the Σ3 grain boundaries to the total length 100% of the CSLgrain boundaries within the above-described specific range, in theintermediate layer forming step, the pressure may be controlled, theaverage thickness of the intermediate layer may be controlled, or aratio of TiCl₄ in the raw material composition may be controlled. Morespecifically, the ratio of the length of the Σ3 grain boundaries in theintermediate layer can be increased by lowering the pressure orincreasing the ratio of TiCl₄ in the raw material composition in theintermediate layer forming step. Further, by increasing the averagethickness of the intermediate layer, the ratio of the length of the Σ3grain boundaries in the intermediate layer can be reduced.

(Upper Layer Forming Step)

As the upper layer, for example, an α-type Al₂O₃ layer formed of α-typeAl₂O₃ (hereinafter, also simply referred to as an “Al₂O₃ layer”) can beformed as follows.

First, the lower layer including one or more Ti compound layers isformed on the surface of the substrate. Then, the intermediate layercontaining TiCNO, TiCO, or TiAlCNO is formed. Of those layers, a surfaceof a layer farthest from the substrate is oxidized. Then, the upperlayer containing the α-type Al₂O₃ layer is formed on the surface of thelayer away from the substrate.

More specifically, the oxidation of the surface of the layer farthestfrom the substrate is performed under conditions that a gas compositionis set to CO₂: 0.3 mol % to 1.0 mol %, H₂: balance, the temperature isset to 950° C. to 1050° C., and the pressure is set to 50 hPa to 70 hPa(oxidation step). The oxidation treatment time at this time ispreferably 1 to 10 minutes.

Then, the α-type Al₂O₃ layer is formed by a chemical vapor depositionmethod in which a raw material gas composition is set to AlCl₃: 2.0 mol% to 5.0 mol %, CO₂: 2.5 mol % to 4.0 mol %, HCl: 2.0 mol % to 3.0 mol%, H₂S: 0.30 mol % to 0.40 mol %, H₂: balance, the temperature is set to950° C. to 1050° C., and the pressure is set to 60 hPa to 80 hPa (filmforming step).

(Outer Layer Forming Step)

Further, the outer layer including a Ti nitride layer (hereinafter, alsoreferred to as a “TiN layer”) or a Ti carbonitride layer (hereinafter,also referred to as a “TiCN layer”) may be formed on a surface of theupper layer.

The TiN layer as the outer layer can be formed by a chemical vapordeposition method in which a raw material composition is set to TiCl₄:7.0 mol % to 8.0 mol %, N₂: 30 mol % to 50 mol %, H₂: balance, thetemperature is set to 950° C. to 1050° C., and the pressure is set to300 hPa to 400 hPa.

The TiCN layer as the outer layer can be formed by a chemical vapordeposition method in which a raw material composition is set to TiCl₄:7.0 mol % to 9.0 mol %, CH₃CN: 0.7 mol % to 2.0 mol %, CH₄: 1.0 mol % to2.0 mol %, N₂: 4.0 mol % to 6.0 mol %, H₂: balance, the temperature isset to 950° C. to 1050° C., and the pressure is set to 60 hPa to 80 hPa.

The thickness of each layer in the coating layer of the coated cuttingtool of the present embodiment can be measured by observing across-sectional structure of the coated cutting tool using an opticalmicroscope, a scanning electron microscope (SEM), a field emissionscanning electron microscope (FE-SEM), and the like. The averagethickness of each layer in the coated cutting tool of the presentembodiment can be obtained as the arithmetic mean value by measuring thethickness of each layer at three or more points in the vicinity of aposition 50 μm from a cutting edge ridgeline portion toward a centerportion of the rake face of the coated cutting tool. Further, thecomposition of each layer in the coating layer of the coated cuttingtool of the present embodiment can be measured from the cross-sectionalstructure of the coated cutting tool by using an energy dispersive X-rayspectroscope (EDS), a wavelength dispersive X-ray spectroscope (WDS),and the like.

It is considered that the coated cutting tool of the present embodimenthas an effect that the tool life can be extended as compared with thatin the related art because the coated cutting tool has excellentfracture resistance and wear resistance. However, factors that canextend the tool life are not limited to the above.

EXAMPLES

Hereinafter, the invention will be described in more detail by way ofExamples, but the invention is not limited to these Examples.

As a substrate, cemented carbide was processed into an insert shape ofCNMG120408, so as to prepare cemented carbide having a composition of89.2WC-8.8Co-2.0NbC (or more mass %). A cutting edge ridgeline portionof the substrate was subjected to round honing with a SiC brush, andthen a surface of the substrate was washed.

[Invention Products 1 to 16 and Comparative Products 1 to 12]

After washing the surface of the substrate, a coating layer was formedby a chemical vapor deposition method. First, the substrate was chargedinto an external thermal chemical vapor deposition device, and underconditions of the raw material gas composition, the temperature, and thepressure shown in Table 1, a lower layer having a composition shown inTable 2 was formed on the surface of the substrate in the order of afirst layer and a second layer so as to have an average thickness shownin Table 2. Then, under conditions of a raw material gas composition, atemperature, and a pressure shown in Table 3, an intermediate layerhaving a composition shown in Table 2 was formed on a surface of thesecond layer of the lower layer so as to have the average thicknessshown in Table 2. Then, a surface of the intermediate layer was oxidizedfor 5 minutes under conditions of a gas composition of CO₂: 0.5 mol %,H₂: 99.5 mol %, a temperature of 1000° C., and a pressure of 60 hPa.Then, under conditions of a raw material gas composition, a temperature,and a pressure shown in Table 1, an upper layer formed of α-typealuminum oxide was formed on the surface of the intermediate layer afterbeing oxidized so as to have an average thickness shown in Table 2.Finally, under conditions of a raw material gas composition, atemperature, and a pressure shown in Table 1, an outer layer having acomposition shown in Table 2 was formed on a surface of the upper layerso as to have an average thickness shown in Table 2. Therefore, coatedcutting tools of Invention Products 1 to 16 and Comparative Products 1to 12 were obtained.

TABLE 1 Composition Temper- Pres- of each ature sure Raw materialcomposition layer (° C.) (hPa) (mol %) Lower TiN 900 350 TiCl₄: 7.5%,N₂: 40.0%, H₂: layer 52.5% TiC 1000 75 TiCl₄: 2.4%, CH₄: 4.6%, H₂: 93.0%TiCN 850 70 TiCl₄: 6.0%, CH₃CN: 1.0%, H₂: 93.0% Upper α-type 1000 70AlCl₃: 2.5%, CO₂: 3.0%, layer Al₂O₃ HCl: 2.3%, H₂S: 0.35%, H₂: 91.85%Outer TiN 1000 350 TiCl₄: 7.5%, N₂: 40.0%, H₂: layer 52.5% TiCN 1000 70TiCl₄: 8.0%, CH₃CN: 1.0%, CH₄: 1.5%, N₂: 5.0%, H₂: 84.5%

TABLE 2 Coating layer Lower layer (Ti Compound layer) Intermediate Firstlayer Second layer Average layer Upper Average Average thickness Averagelayer thickness thickness of entire thickness Crystal Composition (μm)Composition (μm) (μm) Composition (μm) system Invention Product 1 TiN0.1 TiCN 3.2 3.3 TiCNO 1.2 a Invention Product 2 TiN 0.1 TiCN 3.2 3.3TiCNO 0.8 a Invention Product 3 TiN 0.1 TiCN 3.2 3.3 TiCNO 1.6 aInvention Product 4 TiN 0.2 TiCN 2.0 2.2 TiCNO 0.5 a Invention Product 5TiN 0.1 TiCN 3.2 8.0 TiCNO 2.0 a Invention Product 6 TiN 0.1 TiCN 3.23.3 TiCNO 1.0 a Invention Product 7 TiN 0.1 TiCN 3.2 3.3 TiCNO 1.2 aInvention Product 8 TiN 0.1 TiCN 2.0 2.1 TiCNO 1.2 a Invention Product 9TiN 0.1 TiCN 7.8 7.9 TiCNO 1.6 a Invention Product 10 TiN 0.1 TiCN 5.45.5 TiCNO 1.0 a Invention Product 11 TiN 0.1 TiCN 4.0 4.1 TiCNO 1.5 aInvention Product 12 TiN 0.1 TiCN 5.4 5.5 TiCNO 1.2 a Invention Product13 TiN 0.1 TiCN 5.4 5.5 TiCNO 1.2 a Invention Product 14 TiN 0.1 TiCN3.4 3.5 TiCO 1.0 a Invention Product 15 TiN 0.1 TiCN 3.4 3.5 TiAlCNO 1.0a Invention Product 16 TiC 0.1 TiCN 3.2 3.3 TiCNO 1.0 a ComparativeProduct 1 TiN 0.1 TiCN 3.2 3.3 TiCNO 0.5 a Comparative Product 2 TiN 0.1TiCN 3.0 3.1 TiCNO 2.0 a Comparative Product 3 TiN 0.2 TiCN 2.0 2.2TiCNO 0.2 a Comparative Product 4 TiN 0.1 TiCN 3.2 3.3 TiCNO 3.0 aComparative Product 5 TiN 0.1 TiCN 3.2 3.3 TiCNO 1.2 a ComparativeProduct 6 TiN 0.1 TiCN 3.0 3.1 TiCNO 1.2 a Comparative Product 7 TiN 0.1TiCN 1.0 1.1 TiCNO 1.2 a Comparative Product 8 TiN 0.1 TiCN 9.0 9.1TiCNO 1.5 a Comparative Product 9 TiN 0.1 TiCN 5.4 5.5 TiCNO 1.0 aComparative Product 10 TiN 0.1 TiCN 2.2 2.3 TiCNO 1.6 a ComparativeProduct 11 TiN 0.1 TiCN 5.2 5.3 TiCNO 1.2 a Comparative Product 12 TiN0.1 TiCN 3.0 3.1 TiN 1.2 a Coating layer Ratio of average Averagethickness of Upper layer Outer layer thickness intermediate AverageAverage of entire layer to entire thickness thickness coating layercoating layer Composition (μm) Composition (μm) (μm) (%) InventionProduct 1 Al₂O₃ 3.4 TiN 0.3 8.2 14.6 Invention Product 2 Al₂O₃ 3.4 TiN0.5 8.0 10.0 Invention Product 3 Al₂O₃ 3.4 TiN 0.2 8.5 18.8 InventionProduct 4 Al₂O₃ 2.0 TiN 0.3 5.0 10.0 Invention Product 5 Al₂O₃ 6.0 TiN3.0 19.0 10.5 Invention Product 6 Al₂O₃ 3.4 TiN 0.5 8.2 12.2 InventionProduct 7 Al₂O₃ 3.5 TiN 0.5 8.5 14.1 Invention Product 8 Al₂O₃ 3.8 TiCN1.0 8.1 14.8 Invention Product 9 Al₂O₃ 2.2 TiCN 0.5 12.2 13.1 InventionProduct 10 Al₂O₃ 1.0 TiCN 0.5 8.0 12.5 Invention Product 11 Al₂O₃ 6.0TiCN 0.6 12.2 12.3 Invention Product 12 Al₂O₃ 3.0 TiCN 0.5 10.2 11.8Invention Product 13 Al₂O₃ 3.0 TiCN 0.5 10.2 11.8 Invention Product 14Al₂O₃ 3.2 TiCN 0.3 8.0 12.5 Invention Product 15 Al₂O₃ 3.2 TiCN 0.3 8.012.5 Invention Product 16 Al₂O₃ 3.2 TiN 0.5 8.0 12.5 Comparative Product1 Al₂O₃ 3.4 TiN 1.0 8.2 6.1 Comparative Product 2 Al₂O₃ 3.0 TiN 0.2 8.324.1 Comparative Product 3 Al₂O₃ 2.0 TiN 0.6 5.0 4.0 Comparative Product4 Al₂O₃ 6.0 TiN 3.0 15.3 19.6 Comparative Product 5 Al₂O₃ 3.2 TiN 0.58.2 14.6 Comparative Product 6 Al₂O₃ 3.4 TiN 0.5 8.2 14.6 ComparativeProduct 7 Al₂O₃ 4.0 TiCN 1.8 8.1 14.8 Comparative Product 8 Al₂O₃ 1.0TiCN 0.5 12.1 12.4 Comparative Product 9 Al₂O₃ 0.4 TiCN 1.0 7.9 12.7Comparative Product 10 Al₂O₃ 8.0 TiCN 0.3 12.2 13.1 Comparative Product11 Al₂O₃ 3.0 TiCN 0.5 10.0 12.0 Comparative Product 12 Al₂O₃ 3.4 TiN 0.58.2 14.6

TABLE 3 Composition of intermediate Temperature Pressure Raw materialgas composition (mol %) Sample number layer (° C.) (hPa) TiCl₄ CO AlCl₃N₂ HCl H₂ Invention Product 1 TiCNO 1010 100 5.0 1.0 0.0 40.0 3.0 51.0Invention Product 2 TiCNO 1010 100 5.0 1.0 0.0 40.0 5.0 49.0 InventionProduct 3 TiCNO 1010 100 5.0 1.5 0.0 40.0 3.0 50.5 Invention Product 4TiCNO 990 100 4.5 1.0 0.0 60.0 4.0 30.5 Invention Product 5 TiCNO 101080 4.5 1.0 0.0 40.0 3.0 51.5 Invention Product 6 TiCNO 1010 150 5.2 1.50.0 60.0 5.0 28.3 Invention Product 7 TiCNO 1010 100 4.0 1.0 0.0 20.03.0 72.0 Invention Product 8 TiCNO 1030 100 5.0 1.0 0.0 40.0 3.0 51.0Invention Product 9 TiCNO 1010 100 5.0 0.5 0.0 30.0 4.0 60.5 InventionProduct 10 TiCNO 1010 100 5.5 0.8 0.0 50.0 3.0 40.7 Invention Product 11TiCNO 990 80 5.0 1.0 0.0 30.0 3.0 61.0 Invention Product 12 TiCNO 1030120 3.5 1.0 0.0 20.0 2.0 73.5 Invention Product 13 TiCNO 1010 80 5.5 1.00.0 50.0 5.0 38.5 Invention Product 14 TiCO 1010 100 5.0 1.0 0.0 0.0 3.091.0 Invention Product 15 TiAlCNO 1010 100 5.0 0.8 2.5 40.0 5.0 46.7Invention Product 16 TiCNO 1010 100 4.5 1.0 0.0 40.0 3.0 51.5Comparative Product 1 TiCNO 1010 100 5.0 0.5 0.0 30.0 3.0 61.5Comparative Product 2 TiCNO 1010 60 5.0 0.8 0.0 50.0 4.0 40.2Comparative Product 3 TiCNO 950 100 5.0 1.0 0.0 40.0 4.0 50.0Comparative Product 4 TiCNO 1050 80 4.0 0.8 0.0 30.0 2.0 63.2Comparative Product 5 TiCNO 1010 200 5.0 1.0 0.0 70.0 5.0 19.0Comparative Product 6 TiCNO 1010 50 4.0 1.0 0.0 10.0 0.0 85.0Comparative Product 7 TiCNO 1050 100 5.0 1.0 0.0 50.0 8.0 36.0Comparative Product 8 TiCNO 1010 100 5.0 2.0 0.0 40.0 2.0 51.0Comparative Product 9 TiCNO 950 100 5.0 1.0 0.0 40.0 2.0 52.0Comparative Product 10 TiCNO 1010 100 5.0 1.0 0.0 60.0 3.0 31.0Comparative Product 11 TiCNO 1010 150 2.0 1.0 0.0 40.0 3.0 54.0Comparative Product 12 TiN 1010 80 5.0 0.0 0.0 40.0 3.0 52.0

[Average Thickness of Each Layer]

The average thickness of each layer of the obtained sample was obtainedas follows. That is, an arithmetic mean value was obtained as theaverage thickness by measuring thicknesses of three points in a crosssection in the vicinity of a position 50 μm from the cutting edgeridgeline portion of the coated cutting tool toward a center portion ofa rake face using an FE-SEM. Measurement results are shown in Table 2.

[Composition of Each Layer]

The composition of each layer of the obtained sample was measured usingEDS in the cross section in the vicinity of the position 50 μm from thecutting edge ridgeline portion of the coated cutting tool toward thecenter portion of the rake face. Measurement results are shown in Table2.

[Length of CSL Grain Boundaries and Length of Σ3 Grain Boundaries]

The length of CSL grain boundaries and the length of Σ3 grain boundariesof the intermediate layer of the obtained sample were measured asfollows. First, in the coated cutting tool, an observation surface wasobtained by polishing until a cross section of the intermediate layerwas exposed in a direction perpendicular to the surface of thesubstrate. Further, the obtained observation surface was polished usingcolloidal silica to obtain a mirror observation surface.

Then, the above observation surface was observed by an SEM equipped withEBSD. As an observation region, a flank was observed.

As the SEM, SU6600 (manufactured by Hitachi High-Tech Corporation)equipped with EBSD (manufactured by TexSEM Laboratories Inc.) was used.

The normal of the observation surface was tilted 70° with respect to anincident beam, and the analysis was performed by emitting an electronbeam with an acceleration voltage of 15 kV and an irradiation current of1.0 nA. Data collection was performed in steps of 0.1 μm/step for apoint corresponding to a surface region having a length of 80% of thethickness of the intermediate layer×10 μm ((a length of 80% of thethickness of the intermediate layer (μm)×10)×100) on the observationsurface. The data collection was performed for the surface region at 5fields of view (a length of 80% of the thickness of the intermediatelayer×10 μm), and an average value was calculated.

Data processing was performed using commercially available software. CSLcrystal grain boundaries corresponding to any Σ value were counted, andwere confirmed by expressing the ratio of each type of grain boundary asthe ratio to the total crystal grain boundary. From the above, thelength of the Σ3 grain boundaries, the length of the CSL grainboundaries, and the total length of the total grain boundary wereobtained, and the ratio of the length of the CSL grain boundaries to thetotal length 100% of the total grain boundary and the ratio of thelength of the Σ3 grain boundaries to the total length 100% of the CSLgrain boundaries were calculated. Results are shown in Table 4.

TABLE 4 Intermediate layer Ratio of length of Ratio of length of CSLgrain boundaries Σ3 grain boundaries (%) (%) Invention Product 1 40 72Invention Product 2 40 68 Invention Product 3 42 70 Invention Product 428 76 Invention Product 5 47 65 Invention Product 6 22 80 InventionProduct 7 56 61 Invention Product 8 42 68 Invention Product 9 45 68Invention Product 10 36 74 Invention Product 11 46 70 Invention Product12 48 54 Invention Product 13 36 86 Invention Product 14 38 70 InventionProduct 15 40 66 Invention Product 16 38 65 Comparative Product 1 42 68Comparative Product 2 46 72 Comparative Product 3 38 70 ComparativeProduct 4 55 60 Comparative Product 5 14 68 Comparative Product 6 68 57Comparative Product 7 42 74 Comparative Product 8 44 72 ComparativeProduct 9 40 71 Comparative Product 10 38 68 Comparative Product 11 4638 Comparative Product 12 42 72

A cutting test was performed under the following conditions by using theobtained Invention Products 1 to 16 and Comparative Products 1 to 12.Results of the cutting test are shown in Table 5.

[Cutting Test]

Insert: CNMG120408

Substrate: 89.2WC-8.8Co-2.0NbC (or more mass %)

Work material: SUS304P round bar (diameter 150 mm×length 400 mm)

Cutting speed: 200 m/min

Feed rate: 0.30 mm/rev

Depth of cut: 2.0 mm

Coolant: use

Evaluation item: the tool life was defined as when a sample wasfractured or the maximum flank wear width reached 0.3 mm, and themachining time until the tool life was measured.

TABLE 5 Cutting test Sample number Machining time (minutes) InventionProduct 1 24 Invention Product 2 21 Invention Product 3 24 InventionProduct 4 18 Invention Product 5 23 Invention Product 6 22 InventionProduct 7 20 Invention Product 8 18 Invention Product 9 26 InventionProduct 10 19 Invention Product 11 26 Invention Product 12 23 InventionProduct 13 22 Invention Product 14 23 Invention Product 15 24 InventionProduct 16 22 Comparative Product 1 14 Comparative Product 2 15Comparative Product 3 5 Comparative Product 4 12 Comparative Product 514 Comparative Product 6 11 Comparative Product 7 14 Comparative Product8 15 Comparative Product 9 12 Comparative Product 10 15 ComparativeProduct 11 16 Comparative Product 12 9

From results shown in Table 5, in the cutting test, the machining timeuntil the tool life of each Invention Product was “18 minutes” orlonger, which was longer than those of Comparative Products. Therefore,it can be seen that wear resistance and fracture resistance of InventionProducts are generally more excellent than those of ComparativeProducts.

From the above results, it was found that Invention Products haveexcellent wear resistance and fracture resistance, and as a result, havelong tool lives.

INDUSTRIAL APPLICABILITY

Since the coated cutting tool of the invention has extended tool life ascompared with that in the related art by having excellent wearresistance without lowering the fracture resistance, the coated cuttingtool has industrial applicability from such a viewpoint.

REFERENCE SIGNS LIST

1: substrate, 2: lower layer, 3: intermediate layer, 4: upper layer, 5:outer layer, 6: coating layer, 7: coated cutting tool.

What is claimed is:
 1. A coated cutting tool, comprising: a substrate;and a coating layer formed on a surface of the substrate, wherein thecoating layer includes a lower layer, an intermediate layer, and anupper layer in this order from a substrate side to a surface side of thecoating layer, the lower layer includes one or more Ti compound layersformed of a Ti compound containing Ti and at least one element selectedfrom the group consisting of C, N, and B, the intermediate layercontains TiCNO, TiCO, or TiAlCNO, the upper layer contains α-type Al2O3,an average thickness of the lower layer is 2.0 μm or more and 8.0 μm orless, an average thickness of the intermediate layer is 0.5 μm or moreand 2.0 μm or less and is 10% or more and 20% or less of an averagethickness of the entire coating layer, an average thickness of the upperlayer is 0.8 μm or more and 6.0 μm or less, and in the intermediatelayer, a ratio of a length of CSL grain boundaries to a total length100% of a total grain boundary is 20% or more and 60% or less, and aratio of a length of Σ3 grain boundaries to a total length 100% of theCSL grain boundaries is 50% or more and 90% or less, where the CSL grainboundaries include Σ3 grain boundaries, Σ5 grain boundaries, Σ7 grainboundaries, Σ9 grain boundaries, Σ11 grain boundaries, Σ13 grainboundaries, Σ15 grain boundaries, Σ17 grain boundaries, Σ19 grainboundaries, Σ21 grain boundaries, Σ23 grain boundaries, Σ25 grainboundaries, Σ27 grain boundaries, and Σ29 grain boundaries.
 2. Thecoated cutting tool according to claim 1, wherein the ratio of thelength of the Σ3 grain boundaries to the total length 100% of the CSLgrain boundaries is 60% or more and 90% or less.
 3. The coated cuttingtool according to claim 2, wherein the coating layer includes an outerlayer on the upper layer and on a side opposite to the substrate side,the outer layer includes a Ti compound layer formed of a Ti compoundcontaining Ti and at least one element selected from the groupconsisting of C, N, and B, and an average thickness of the outer layeris 0.2 μm or more and 4.0 μm or less.
 4. The coated cutting toolaccording to claim 3, wherein the substrate is any one of cementedcarbide, cermet, ceramics, or a cubic boron nitride sintered body. 5.The coated cutting tool according to claim 3, wherein the averagethickness of the entire coating layer is 5.0 μm or more and 20.0 μm orless.
 6. The coated cutting tool according to claim 5, wherein the Ticompound layer included in the lower layer is at least one selected fromthe group consisting of a TiN layer formed of TiN, a TiC layer formed ofTiC, a TiCN layer formed of TiCN, and a TiB2 layer formed of TiB2. 7.The coated cutting tool according to claim 6, wherein the substrate isany one of cemented carbide, cermet, ceramics, or a cubic boron nitridesintered body.
 8. The coated cutting tool according to claim 2, whereinthe average thickness of the entire coating layer is 5.0 μm or more and20.0 μm or less.
 9. The coated cutting tool according to claim 2,wherein the Ti compound layer included in the lower layer is at leastone selected from the group consisting of a TiN layer formed of TiN, aTiC layer formed of TiC, a TiCN layer formed of TiCN, and a TiB2 layerformed of TiB2.
 10. The coated cutting tool according to claim 2,wherein the substrate is any one of cemented carbide, cermet, ceramics,or a cubic boron nitride sintered body.
 11. The coated cutting toolaccording to claim 1, wherein the coating layer includes an outer layeron the upper layer and on a side opposite to the substrate side, theouter layer includes a Ti compound layer formed of a Ti compoundcontaining Ti and at least one element selected from the groupconsisting of C, N, and B, and an average thickness of the outer layeris 0.2 μm or more and 4.0 μm or less.
 12. The coated cutting toolaccording to claim 11, wherein the average thickness of the entirecoating layer is 5.0 μm or more and 20.0 μm or less.
 13. The coatedcutting tool according to claim 11, wherein the Ti compound layerincluded in the lower layer is at least one selected from the groupconsisting of a TiN layer formed of TiN, a TiC layer formed of TiC, aTiCN layer formed of TiCN, and a TiB2 layer formed of TiB2.
 14. Thecoated cutting tool according to claim 11, wherein the substrate is anyone of cemented carbide, cermet, ceramics, or a cubic boron nitridesintered body.
 15. The coated cutting tool according to claim 1, whereinthe average thickness of the entire coating layer is 5.0 μm or more and20.0 μm or less.
 16. The coated cutting tool according to claim 15,wherein the Ti compound layer included in the lower layer is at leastone selected from the group consisting of a TiN layer formed of TiN, aTiC layer formed of TiC, a TiCN layer formed of TiCN, and a TiB2 layerformed of TiB2.
 17. The coated cutting tool according to claim 15,wherein the substrate is any one of cemented carbide, cermet, ceramics,or a cubic boron nitride sintered body.
 18. The coated cutting toolaccording to claim 1, wherein the Ti compound layer included in thelower layer is at least one selected from the group consisting of a TiNlayer formed of TiN, a TiC layer formed of TiC, a TiCN layer formed ofTiCN, and a TiB2 layer formed of TiB2.
 19. The coated cutting toolaccording to claim 18, wherein the substrate is any one of cementedcarbide, cermet, ceramics, or a cubic boron nitride sintered body. 20.The coated cutting tool according to claim 1, wherein the substrate isany one of cemented carbide, cermet, ceramics, or a cubic boron nitridesintered body.